Detailed explanation of waterproof and breathable fabric lamination technology and waterproof and breathable fabric expansion technology

1. The concept of fabric and film interface
From the perspective of three-layer composite fabrics, waterproof and breathable laminated fabrics are composed of one or more layers of fabric and polymer films bonded together through adhesives to form a composite fabric with multiple functions. No matter how good the performance of the fabric and film is, if it cannot be bonded well to form a whole, or the peeling resistance of the laminated fabric after bonding is poor, it is obvious that this fabric has no practical value. The structural properties of the interface are closely related to the bonding effect. The stress on the fabric or film will be transmitted to each other through the interface between them, forming an overall macroscopic mechanical behavior.
The interface is not a single bonding surface, but rather a layer of different thicknesses and different functional areas and interfaces. The interface layer of the three-layer composite fabric laminated fabric is composed of the fabric surface area, the interaction area between the fabric and the film, the film surface area and the multi-layer transition area. For the part where adhesive exists, the original interaction zone is expanded into a multi-layer bonding zone.
At the macro level, the concepts of surface, interface or contact are very clear, and boundary crossings are easily determined. But when discussing the interaction between contact surfaces, it is a micro-level concept, and the division of the surface or interface is not so clear. The surface area refers to a thin layer with asymmetric structure and obviously different properties from the main body. These are difficult to distinguish from the microscopic level. Even in a certain layer area, the structure is not a homogeneous phase, and there are also heterogeneous heterostructure micro-areas.

2. Interface force and bonding strength
The force on the bonding interface is directly related to the bonding strength. Kunshan Yingjie Textile Import and Export Co., Ltd. believes that there are three types of forces on the interface: one is static force, such as the force generated by “anchoring” and friction, the so-called The “anchoring” effect is due to the uncured resin flowing into the pits or gaps of the bonding part and solidifying there. Its effect is equivalent to anchoring a ship to fix the resin on the surface of the bonding body. The contribution of this kind of static force to the interface bonding strength theoretically reaches 1.4~7.0MPa. The second type is the interfacial intermolecular force, that is, when the adhesive and the adherend are close to each other, it is 0.3~0.5nm. The force generated by dispersion, dipole and hydrogen bonding can theoretically contribute up to 7.0x102MPa to the interface bonding strength. The third type is chemical bonding force, that is, when the adhesive molecules and the adherend molecules are close to each other within 0.1~0.3 nm, a chemical reaction occurs to form a chemical bond. The contribution of this chemical bond to the interface bonding strength can theoretically reach 7.0×103~7.0x104MPa . These three types of forces may exist simultaneously for a bonding system, but their effects vary depending on the situation. Generally speaking, the intermolecular force contributes a large proportion to the interface bonding strength, but the ability to resist medium and water corrosion mainly depends on the chemical bond force. Therefore, in order to make the interface bonding strength both high and resistant to medium corrosion, In addition to sufficient intermolecular forces, the interface must introduce necessary chemical bonding forces. From the above analysis, it can be seen that if the interface is ideally bonded, the interface bonding strength is very considerable. In fact, the bonding strength retains a very small part of the theoretical value. This is due to poor intermolecular contact during the bonding process, which results in microporous defects on the bonding interface, reduces the bonding interface area, causes stress concentration, and promotes early failure. In addition, the residual thermal stress and shrinkage stress at the interface also contribute to strength loss.

3. Introduction to waterproof, moisture-permeable and expandable fabrics
Ordinary fibers are coated with swollen polymers on the outer layer. After being woven into fabric, they become moisture-permeable when dry and waterproof when exposed to water.
Swelling polymers usually use hydrogels. Hydrogels have the characteristics of swelling by absorbing water and deswelling by dehydration, and are grafted and polymerized on fabrics. In a dry state, the grafted gel layer shrinks, and the large number of gaps on the fabric can ensure the permeation of sweat emitted by the human body, meeting the requirements of wearing comfort; when immersed in water, the grafted gel layer swells rapidly, The pores are closed, thus providing good waterproof or immersion resistance. Through the action of this driving mechanism, the two properties of “waterproof” and “moisture permeability” can be satisfied accordingly under different environmental conditions.
Someone chose the method of electron beam pre-irradiation to graft-polymerize acrylic monomer onto polyester fabric, and studied the properties of the fabric. The test results show that when acrylic acid is grafted on the fabric, the fabric has water-blocking ability within 3S. The greater the grafting rate of the fabric, the faster it responds to water, and as time goes by, the water-blocking ability continues to improve. rise until it reaches a certain value.
In recent years, with the in-depth understanding of the properties of PTFE and the improvement of film-making technology, laminated fabrics of functional fabrics have been developed based on the second functional fabric. For example: waterproof, breathable and elastic fabrics, waterproof, breathable and flame-retardant composite fabrics, waterproof, breathable and moisturizing fabrics, radiation protection clothing fabrics, etc.

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